Lighting fixtures that utilize light emitting diodes as a light source are increasingly desirable, particularly in outdoor lighting environments. There is a need to control the direction and intensity of light output by such fixtures. For example, achieving the high optical performance required for roadway lighting demands reduction in glare to pedestrians and motorists and uplight pollution produced by the lighting fixture, while maximizing horizontal surface illumination and maintaining a smooth illumination distribution. There are different lighting configurations, for example in roadway and parking lot applications.
In roadway lighting, depending on the position of the lighting fixture and area of the roadway to be illuminated it is desirable to control the intensity of the light along the roadway with minimal light in other directions. In controlling the light along the roadway, it is desirable to provide a relatively uniform distribution of light along the roadway where desired.
In the field of parking lot lighting, is also desirable to control the direction and intensity of the light emitted by a lighting fixture. For example, if a lighting fixture is mounted to a building, any substantial light in a direction towards the building would be undesirable and inefficient. It is desirable that the light emitted by the fixture is most efficiently used in lighting the parking lot.
Conventional outdoor lighting fixtures are of a wide variety of constructions and designs. Single source lamps, such as incandescent bulbs, tungsten and halogen bulbs, are used. While being low in initial cost, it is difficult to control the direction of the light emitted therefrom and illuminate different directions with different sources of light. Generally, the single source lamps radiate light all the way around the lamp and also over the distance of the filament, for example, over the length of an elongated are tube. Another type of single source lamps are fluorescent bulbs which are more efficient but are bulky, fragile and require a starter circuit. Both of these sources of light are difficult to control since they generate light over a distance and radiate in all directions.
More recently, light emitting diodes (LEDs or emitters) have been used as a light source for outdoor lighting fixtures. An emitter is a relatively good source of bright and efficiently produced light, and emitter technology is advancing rapidly. It is recognized that emitters generate substantial heat that, if not dissipated, can shorten the life span of the emitter.
In various outdoor lighting applications it is desirable to light specific predetermined areas. For example, in street lighting it may be desirable to light specific areas, such as along the roadway, and not light or provide low level light to other areas. In other applications, such as in a parking lot where the outdoor lighting fixture is adjacent to a building, it is desirable to provide light to the parking lot but minimal, if any, light to the roof of the building. In other applications, light directed to other areas may not only be undesirable from an efficiency stand point but also be a nuisance depending on the position of the lighting fixture.
The directional light characteristics of LEDs are known. Bagemann U.S. Pat. No. 6,250,774 provides for rotation of LEDs to direct the light emitted from the LEDs. Bagemann shows street lighting fixture with lighting units, each having an LED and an associated reflector/refractor/diffractor. The LEDs may be rotated to direct the light in different directions. The LEDs are pivotally mounted on a housing and independently movable to direct the light emitted from the LED associated with the reflector/refractor in different directions. By rotating the LED lens unit, the direction of the light can be changed.
Frecska, U.S. Pat. No. 7,311,423, shows LEDs mounted on a support member which is rotatable to change the direction of light emitted from the LEDs. Diffuser lenses are provided for diffusing the light rays for indirect lighting. Kishimura, U.S. Pat. No. 6,942,361, also shows a street lighting fixture utilizing LEDs.
Dry in U.S. Pat. Nos. 6,815,724, 6,831,303, 7,242,028, 7,288,796, 6,573,536, and US Patent Application Publications 2003/230765, 2004/026721, 2004/141326, 2005/258439, 2005/258440, 2005/269581 provide an octagonal tower on which LEDs are mounted to the tower. Air flows through the tower and carries away some of the heat generated by the LEDs.
Additional approaches providing LEDs in lighting fixtures are known. For example, in Mighetto, U.S. Pat. No. 7,387,403, a plurality of modular lighting element subassemblies each carrying an LED are coupled into modular stacked frames at locations of the users selection and electrically connected using interconnects such as conductors. In Hong, U.S. Pat. No. 6,621,122, a light emitting circuit assembly is formed of a hollow polygonal circuit board in a rectangular, triangular or hexagonal profile, with a plurality of LEDs in each of its peripheral walls.
Depicted in Moore, U.S. Pat. No. 6,668,752, is a two dimensional array of LEDs controlled by a microprocessor running a computer program that illuminates the LEDs in a sequence to simulate a flame. The array of LEDs is arranged on the surface of a cylinder or several flat surfaces forming a faceted tube.
In U.S. Pat. No. 6,715,900 and US Publication No. 2004/0165387, both to Zhang, a luminary unit has a plurality of LEDs on the peripheral surface of a supporting frame.
It is desirable to improve the efficiency of a lighting fixture and use the light generated by the lighting fixture to light only the desired area or areas. It is also desirable to provide a lighting fixture that provides relatively uniform illumination over the area to be illuminated. It is further desirable to configure the direction and amount of light provided by a lighting fixture to achieve a desired lighting distribution.
Various other desirable features are set forth in the following brief description of the drawings, the description of the preferred embodiments, and the appended claims.